Pneumatic tires usually contain innerliner layers to retard permeation of air from the tire's cavity into the tire carcass. Such innerliner, or barrier, layers are usually in a form of layers comprised of butyl rubber or halogenated butyl rubber (sometimes referred to as halobutyl rubber) based rubber compositions which provide resistance to permeability of air.
To adequately promote resistance to air permeability, such innerliner is typically provided as a sufficiently thick layer which, in turn, may add significant weight to the tire.
Accordingly, various alternative thin air permeability resistant films have been proposed for pneumatic tire innerliners which are significantly lighter in weight. For example, and not intended to be limiting, see U.S. Pat. Nos. 4,928,741, 5,040,583, 5,938,869, 6,359,071, 6,376,598, 6,843,292, 6,861,470 and 8,544,517; U.S. Patent Publication Nos. 2001/0041762, 2013/0101821, 2013/0192736, 2013/0199686, 2014/0227499 and 2014/0242370; PCT Patent Publication Nos. WO/2007/050061, WO/2007/050236, WO/2007/070728, WO/2007/111584, WO/2008/051253, and European Patent Publication Nos. EP 0706878, EP 0722850, EP 1726620 and EP 1880871.
Various thin films of various polymers have been proposed for a tire innerliner layer comprised of, for example, a combination of thermoplastic resin which may contain a blend or dispersion of various polymers or copolymers. The such films may be provided, for example, with a coating on both of its sides with an RFL (resorcinol/formaldehyde latex based) adhesive to promote adhering of overlapping ends of the film together, particularly where the film is placed on the circumferential inner surface of the tire.
For this invention, it is desired to provide a pneumatic tire having an innerliner to promote a combination of adaption to the tire's rubber carcass and to promote resistance to air permeation.
For such challenge, such innerliner is proposed as a non-spliced, multilayered continuous laminate of a plurality of film layers with varied individual film layer moduli which extends in a circumferential direction to cover the inner surface of the of the tire's rubber carcass (the surface of the pneumatic tire's carcass facing its air chamber with the innerliner therebetween). Such proposed innerliner is a laminate of films with individually or collectively graduated, alternating, random, or their combination of individual film layer moduli of the innerliner multi-layered laminate film.
In one embodiment, the innermost film layer of said innerliner laminate (facing the tire carcass) contains a thin RFL coating on its surface adjacent to the tire rubber carcass (to promote adherence of the film laminate to the tire rubber carcass).
In one embodiment, the innermost film layer of said innerliner laminate has a film modulus lower than the film modulus of the film laminate to promote physical compatibility of the film laminate with the surface of tire rubber carcass (through the RFL coating).
In one embodiment, for such challenge, it is proposed to provide such innerliner laminate with its multiple film layers having directionally increasing film layer moduli, alternate film layer moduli, random film layer moduli and their combination with the innermost film of the laminate (facing the tire rubber carcass through the aforesaid RFL coating) having a film modulus lower than the film modulus of the film laminate.
In one embodiment, the innerliner film laminate is comprised of at least 2, alternately at least 4, of the film layers. In one embodiment, the innerliner film laminate is comprised of a range of from 2 through about 30, alternately from 4 through about 15, of the film layers.
The laminate may be provided, for example, as an extrusion of a laminate comprised of the said film layers and thereby a film layered laminate extrusion, such as, for example, by blow molding to form a tubular shaped laminate of a desired diameter which may then be cut into individual seamless (non-spliced) hoops of the laminate.
The film layers of the laminate are comprised of a thermoplastic polyamide-based polymer which contains dispersed polymer domains therein where said dispersed domains are composed of a blend of copolymer comprised of a polyamide based segment and a polyoxyalkylene diamine.
The modulus of the laminate (which might be referred to herein as a film modulus) is presented by ASTM D882 Test at a 25 percent strain (23° C.) using a cross head speed of 300 mm/min and reported in terms of MPa (megapascals) stress under such conditions. For the test, the laminate is clamped (gripped) between two clamps spaced apart from each other by 30 mm and then stretched in the direction of its formative extrusion (in the laminate's direction of formation by extrusion from an extruder). The overall film modulus of the multilayered film laminate may be tested in this manner. The individual film layers of the multilayered film laminate might be individually formed and submitted to the film modulus test by, for example, individually extruding each film layer and testing each individually extruded film in this manner.
The outermost and innermost surfaces of the multilayered film laminate may be tested for their hardness where, in one embodiment it may be desired that the hardness of the innermost film layer (the laminate's film layer facing the tire's rubber carcass) is softer than the outermost film layer of the laminate. A suitable hardness test is an instrumented indentation test as ASTM Test E2546-7. A descriptive “Introduction to Instrumented Indentation Testing” by J. Hay may be found in Experimental Techniques, Pages 66 through 72, November/December 2009, Society for Experimental Mechanics. The indentation test reportedly may be used for testing thin films to measure hardness (H) and Young's modulus (E) as a relationship between stress and strain for small volumes of films when the film deformation is elastic.
The multilayered innerliner film may be prepared, for example, by co-extrusion of the polyamide-based polymer containing various levels of the dispersed domains to provide the physical moduli of the individual co-extruded film layers. For example, a higher level (an increased domain concentration) could be used to provide a decreased film modulus of an individual film of the film laminate.
In practice, as indicated, the multilayered innerliner film laminate may be blow molded and tubular film then sliced to form individual hoops of the multilayered film of desired diameters. The seamless hoop of the laminate may be positioned on a tire building drum and the tire built thereover.
A significant aspect of the invention is providing an innerliner multilayer film laminate, and tire with such multilayered film laminate innerliner, positioned continuously and circumferentially around the tire inner surface comprised of a plurality of film layers of cooperative varying moduli without a splice to disrupt the complex layered moduli rheology of the laminate and air permeability innerliner by an abutted or overlapped splice which would in turn provide the laminate with discontinuous and likely miss-matched ends of multiple layers of the varied film layer moduli and thereby provide generally unwanted varied air permeability resistance across the width of the innerliner laminate at such splice.